The objectives of this proposal are to uncover the species diversity of pomatiopsid snails in the Yangtze River drainage and the diversity of species of Schistosoma and paragonimus that have coevolved with these snails over the past 10 to 14 million years. Objectives are 1) to sequence the mitochondrial cytochrome b gene of diverse species of pomatiopsid snails (Pomatiopsinae and Triculinae) from targeted provinces to establish a molecular-based phylogeny to compare with the extant anatomy-based phylogeny; 2) to use cDNA from oncomelania hupensis to sequence the DNA of specific genes to determine the degree and pattern of population divergence of oncomelania throughout China. The data will be used to test the hypothesis that the genetic divergence of oncomelania populations is paralleled by genetic divergence of S. japonicum transmitted by those snail populations; 3) to sequence snail genes whose homologues in S. japonicum and paragonimus skrjabini show intraspecific population divergence in order to calibrate a co-evolved molecular clock, in part to determine the extent to which parasite pressure drives snail evolution (our hypothesis is that it does to a considerable extent in oncomelania) and the extent to which snail evolution pressures schistosome evolution; 3) to indicate to those of this TMRC who are wording on the genetic divergence of S. japonicum when a population of oncomelania has diverged genetically to such an extent that it is worth examining the genetics of the S. japonicum population transmitted by the snail population; 4) to examine the genetics of snail populations brought to our attention by those of the TMRC project 1 who have found a genetically diverse population of parasite of either S. japonicum or paragonimus spp. that would suggest a parallel genetic differentiation in the snail population; 5) to do the basic systematic word-up of undescribed species involved in the transmission of Paragonimus.